CN103541727A - Deepwater shallow layer fracture pressure computing technology - Google Patents

Abstract

The invention discloses a deepwater shallow layer fracture pressure computing technology, and relates to the technical field of petroleum drilling. By means of the deepwater shallow layer fracture pressure computing technology, a method for computing shallow layer fracture pressure in the deepwater drilling process is provided. The method includes the following steps that the mechanical property of a deepwater shallow layer stratum is determined according to earthquake interval velocity data and test data; the stress state of a plastic zone around a well in the well pressurizing process is computed using a unified strength criterion as the yield criterion; the excess pore pressure distribution law caused by drilling after the well is drilled is computed by combining the excess pore pressure theory in soil mechanics; the effective stress around the well is computed according to the Terzaghi effective stress theory; the fracture pressure of the deepwater shallow layer stratum is computed by combining the hydrofracture theory. The method is a novel method which is proposed based on deepwater shallow layer stratum mechanical parameter laboratory experimental measurement and combined with site physical conditions, and by the way of testing site practical situations, the method has a good application effect.

Description

Deep water shallow-layer fracture pressure computing technique

Technical field

The present invention relates to petroleum drilling technology field, be specifically related to deepwater drilling superficial part formation fracture pressure and determine technology.

Background technology

Along with land unexplored field is fewer and feweri, offshore oil exploration and exploitation has become a hot fields of each major oil companies' competition of the world.According to statistics, 2000-2005, the newly-increased oil gas proved reserves 164 * 108t oil equivalent in the whole world, its mesopelagic (200 meter Dao1000 meter Shui Shen) accounts for 41%, and shallow sea accounts for 31%, landly accounts for 28%; The petroleum reserves that the whole world is verified at the beginning of 2009 is 13,420 hundred million barrels, and wherein deep water accounts for 10%, over 100,000,000,000 barrels.Deep water field is the developing direction of following petroleum exploration and development, and Deep In The Ocean is carried out the development trend that oil-gas exploration and development is World Oil Industry.

But deepwater drilling cost is high, within average day, take more than 1,000,000 dollars, controlling drilling cost is the key that improves oil field development economic benefit.Be subject to the impact of the depth of water, deep water stratum overburden pressure is low, during the low drilling well of well fracture pressure, very easily misses, and affects safety drilling and drilling cost.

The not yet fixed diagenesis in deep water superficial part stratum, is controlled by the theory of consolidation of saturated soil, and the borehole wall can enter plastic state before breaking, and existing fracture pressure model is all based upon on Elasticity basis, cannot disclose its failure mechanism.To the calculating of deep water shallow-layer fracture pressure, be all based on the real empirical model that bores statistics in scene at present both at home and abroad, these models are all only applicable to the more ripe deep water hydrocarbon field of exploitation, for this deep water block that has just dropped into exploitation of South China Sea deep water sea area, do not have enough measured datas to set up empirical model, need to set up a kind of theoretical model that can calculate all deep water hydrocarbons field fracture pressure from the mechanical state on stratum.

Summary of the invention

The computational methods that the object of this invention is to provide deepwater drilling process middle-shallow layer fracture pressure, utilize the method to calculate simply, accurately the fracture pressure on deep water superficial part stratum, and result of calculation is accurate.

Utilize above-mentioned purpose, the present invention adopts following technical scheme:

Deep water shallow-layer fracture pressure computing technique, the application process of this technology comprises step:

(1) according to seismic interval velocity data and experimental data, determine deep water superficial part formation mechanical property;

(2) take unified failure criterion calculates the well week plastic zone stress state in well pressure process as yield criterion;

(3) according to the theoretical well brill that calculates of the excess pore pressure in soil mechanics, open the excess pore pressure regularity of distribution that rear drilling well causes;

(4) according to the theoretical effective stress of calculating wellbore of effective stress;

(5) in conjunction with the theoretical fracture pressure of calculating deep water superficial part stratum of fracturing.

Wherein, the experimental analysis of deep water superficial part formation mechanical property adopts GB < < Standard for test methods of earthworks (GB_T50123-19993) > >.

Wherein, deep water superficial part stratum is elastic-perfectly plastic material, supposes that deep water superficial part stratum is homogeneous, isotropic elastic-perfectly plastic material, and well is bored and opened front stratum is elastic stage, and unified failure criterion is obeyed in the surrender on stratum

σ _r＝Mσ _θ+σ ₀ (1)

Wherein,

In formula: b (0≤b≤1) is the parameter of reaction intermediate principal stress impact; M is intermediate principal stress coefficient, m≤1 in plane strain situation, and m < 1 under elastic stage, enters m under plastic state and levels off to 1, and in this article, when the deep water shallow-layer soil body enters after plastic state, m value gets 1; C,

cohesion while being respectively saturated not draining of the soil body and angle of internal friction, adopt total stress Shear Strength Index.

Deep water shallow-layer fracture pressure design formulas is

$P_f=\frac{2M({\mathrm{\&sigma;}}_h-P_{p0}+\mathrm{St})}{(1.73A+0.42)(M-1)}-\frac{{\mathrm{\&sigma;}}_0}{M-1}---\left(4\right)$

In formula, P _ffor fracture pressure; σ _hfor stress flatly;

for pore pressure; St is stratum tensile strength; A is Skempton excess pore pressure coefficient.

Deep water shallow-layer Fracturing Pressure Prediction technology provided by the invention, be suitable for the prediction to superficial part formation fracture pressure in deepwater drilling process, the method is the new method proposing in conjunction with on-the-spot physical condition on the basis of measuring at deep water superficial part formation force mathematic(al) parameter laboratory experiment, through on-site actual situations check, there is good effect.

Accompanying drawing explanation

Fig. 1 is the mechanical model figure while calculating deep water shallow-layer fracture pressure, and Fig. 2 is the flow chart of deep water shallow-layer fracture pressure computing technique of the present invention.

The specific embodiment

The method of the calculating deep water shallow-layer fracture pressure that the present invention proposes, is described as follows in conjunction with the accompanying drawings and embodiments.

The stratum of wellbore is subject to the effect of geostatic stress and wellbore pressure, after well is drilled to, in wellbore, cause stress redistribution, the stress that forms wellbore is concentrated, the not yet fixed diagenesis in deep water superficial part stratum, controlled by the theory of consolidation of saturated soil, the borehole wall can enter plastic state before breaking, and the stratum beyond plastic zone is still in elastic stage.

Wherein, the experimental analysis of deep water superficial part formation mechanical property adopts GB < < Standard for test methods of earthworks (GB_T50123-19993) > >.

The deep water superficial part sedimentation time is short, and the tectonic movement of experience is few, and stratum poisson's ratio is larger, makes flatly between stress difference little, can think and be subject to evenly flatly effect of stress, and before well is bored and opened, stratum is subject to overburden pressure σ _veven stress σ flatly _heffect.

Deep water superficial part stratum is elastic-perfectly plastic material, supposes that deep water superficial part stratum is homogeneous, isotropic elastic-perfectly plastic material, and well is bored and opened front stratum is elastic stage, and unified failure criterion is obeyed in the surrender on stratum

σ _r=Mσ _θ+σ ₀ (1)

Wherein,

In formula: b (0≤b≤1) is the parameter of reaction intermediate principal stress impact; M is intermediate principal stress coefficient, m≤1 in plane strain situation, and m < 1 under elastic stage, enters m under plastic state and levels off to 1, and in this article, when the deep water shallow-layer soil body enters after plastic state, m value gets 1; C,

cohesion while being respectively saturated not draining of the soil body and angle of internal friction, adopt total stress Shear Strength Index.

In drilling process, because drilling fluid can form the mud cake of one deck densification on the borehole wall, stop the fluid seepage flow of pit shaft and ground interlayer, can think that small deformation is obeyed in the not draining of the shallow-layer soil body, the distortion of the soil body theoretical.Well is bored the change that meeting causes well week reservoir stress, and due to not draining of the soil body, part stress can the pore pressure in stratum be born, and causes the change of formation pore pressure.By changed the pore pressure change amount causing by external applied load, be called excess pore pressure, be denoted as Δ P, its expression formula is

ΔP=P _p-P _p0=βΔσ _oct+(2.12A-0.71)Δτ _oct (4)

Wherein,

$\mathrm{\&Delta;}{\mathrm{\&sigma;}}_{\mathrm{oct}}=\frac{1}{3}({\mathrm{\&Delta;\&sigma;}}_1+{\mathrm{\&Delta;\&sigma;}}_2+{\mathrm{\&Delta;\&sigma;}}_3)---\left(5\right)$

${\mathrm{\&Delta;\&tau;}}_{\mathrm{oct}}=\frac{1}{3}\sqrt{{({\mathrm{\&Delta;\&sigma;}}_1-{\mathrm{\&Delta;\&sigma;}}_2)}^2+{({\mathrm{\&Delta;\&sigma;}}_2-{\mathrm{\&Delta;\&sigma;}}_3)}^2+{({\mathrm{\&Delta;\&sigma;}}_3-{\mathrm{\&Delta;\&sigma;}}_1)}^2}---\left(6\right)$

In formula: α and β are Henkel pore pressure coefficient, for saturated soil, get β=1; A is Skempton excess pore pressure coefficient.

In drilling process, according to mechanical balance equation, at any point place, the stress of the shallow-layer soil body has following relation

$\frac{{\mathrm{d\&sigma;}}_r}{\mathrm{dr}}+\frac{{\mathrm{\&sigma;}}_r-{\mathrm{\&sigma;}}_{\mathrm{\&theta;}}}{r}=0---\left(7\right)$

In formula: σ _r, σ _θbe respectively radial stresses and shear stress.

Utilize formula (1), formula (7) and fringe conditions

the Stress Field Distribution that can obtain plastic region is

$\left.\begin{array}{c}{\mathrm{\&sigma;}}_r=(P_w+\frac{{\mathrm{\&sigma;}}_0}{M-1}){\left(\frac{r_w}{r}\right)}^{\frac{M-1}{M}}-\frac{{\mathrm{\&sigma;}}_0}{M-1}\\ {\mathrm{\&sigma;}}_z=\frac{M+1}{2M}(P_w+\frac{{\mathrm{\&sigma;}}_0}{M-1}){\left(\frac{r_w}{r}\right)}^{\frac{M-1}{M}}-\frac{{\mathrm{\&sigma;}}_0}{M-1}\\ {\mathrm{\&sigma;}}_{\mathrm{\&theta;}}=\frac{1}{M}(P_w+\frac{{\mathrm{\&sigma;}}_0}{M-1}){\left(\frac{r_w}{r}\right)}^{\frac{M-1}{M}}-\frac{{\mathrm{\&sigma;}}_0}{M-1}\end{array}\right\}---\left(8\right)$

According to plastic zone stressometer formula (8), the plastic zone stress increment being caused by drilling well is

$\left.\begin{array}{c}\mathrm{\&Delta;}{\mathrm{\&sigma;}}_r=(P_w+\frac{{\mathrm{\&sigma;}}_0}{M-1}){\left(\frac{r_w}{r}\right)}^{\frac{M-1}{M}}-\frac{{\mathrm{\&sigma;}}_0}{M-1}-{\mathrm{\&sigma;}}_h\\ {\mathrm{\&Delta;\&sigma;}}_z=\frac{M+1}{2M}(P_w+\frac{{\mathrm{\&sigma;}}_0}{M-1}){\left(\frac{r_w}{r}\right)}^{\frac{M-1}{M}}-\frac{{\mathrm{\&sigma;}}_0}{M-1}-{\mathrm{\&sigma;}}_h\\ \mathrm{\&Delta;}{\mathrm{\&sigma;}}_{\mathrm{\&theta;}}=\frac{1}{M}(P_w+\frac{{\mathrm{\&sigma;}}_0}{M-1}){\left(\frac{r_w}{r}\right)}^{\frac{M-1}{M}}-\frac{{\mathrm{\&sigma;}}_0}{M-1}-{\mathrm{\&sigma;}}_h\end{array}\right\}---\left(9\right)$

According to the method for average on stratum, formula (9) computational plasticity district to STRESS VARIATION amount Δ σ _octwith average shear stress variation delta τ _oct, then substitution formula (4) gets final product to such an extent that plastic zone excess pore pressure is

$\mathrm{\&Delta;P}=\frac{(1.73A+0.42)(M-1)+2}{2M}(P_w+\frac{{\mathrm{\&sigma;}}_0}{M-1}){\left(\frac{r_w}{r}\right)}^{\frac{M-1}{M}}-\frac{{\mathrm{\&sigma;}}_0}{M-1}-{\mathrm{\&sigma;}}_h---\left(10\right)$

According to Terzaghi principle of effective stress, plastic zone effective stress can be expressed as

$\left.\begin{array}{c}{{\mathrm{\&sigma;}}^{\&prime;}}_r={\mathrm{\&sigma;}}_r-\mathrm{\&Delta;P}-P_{p0}=\frac{(1.58-1.73A)(M-1)}{2M}(P_w+\frac{{\mathrm{\&sigma;}}_0}{M-1}){\left(\frac{r_w}{r}\right)}^{\frac{M-1}{M}}+{\mathrm{\&sigma;}}_h-P_{p0}\\ {{\mathrm{\&sigma;}}^{\&prime;}}_{\mathrm{\&theta;}}={\mathrm{\&sigma;}}_{\mathrm{\&theta;}}-\mathrm{\&Delta;P}-P_{p0}=\frac{-(1.73A+0.42)(M-1)}{2M}(P_w+\frac{{\mathrm{\&sigma;}}_0}{M-1}){\left(\frac{r_w}{r}\right)}^{\frac{M-1}{M}}+{\mathrm{\&sigma;}}_h-P_{p0}\\ {{\mathrm{\&sigma;}}^{\&prime;}}_z={\mathrm{\&sigma;}}_z-\mathrm{\&Delta;P}-P_{p0}=\frac{(0.58-1.73A)(M-1)}{2M}(P_w+\frac{{\mathrm{\&sigma;}}_0}{M-1}){\left(\frac{r_w}{r}\right)}^{\frac{M-1}{M}}+{\mathrm{\&sigma;}}_h-P_{p0}\end{array}\right\}---\left(11\right)$

When the pore pressure in deep water shallow-layer saturated soil body unit equals to act on the external pressure on this element, the soil body is in critical condition, when pore pressure surpasses threshold, effective stress in the soil body will become tensile stress, if tensile stress surpasses the tensile strength of the soil body, to ftracture in stratum, wellbore pressure is now just fracture pressure.

When breaking, pit shaft should meet fringe conditions

${{\mathrm{\&sigma;}}^{\&prime;}}_{\mathrm{\&theta;}}{|}_{{r=r}_w}=-\mathrm{St}---\left(12\right)$

In formula, St is stratum tensile strength.

The tangential effective stress being obtained on the borehole wall by formula (11) is

${{\mathrm{\&sigma;}}^{\&prime;}}_{\mathrm{\&theta;}}{|}_{{r=r}_w}=\frac{-(1.73A+0.42)(M-1)}{2M}(P_w+\frac{{\mathrm{\&sigma;}}_0}{M-1})+{\mathrm{\&sigma;}}_h-P_{p0}---\left(13\right)$

Formula (11) substitution formula (10) can be obtained to deep water shallow-layer pit shaft fracture pressure is

$P_f=\frac{2M({\mathrm{\&sigma;}}_h-P_{p0}+\mathrm{St})}{(1.73A+0.42)(M-1)}-\frac{{\mathrm{\&sigma;}}_0}{M-1}---\left(14\right)$

Above embodiment is only for illustrating the present invention; and be not limitation of the present invention; the those of ordinary skill in relevant technologies field; without departing from the spirit and scope of the present invention; can also make a variety of changes and modification; therefore all technical schemes that are equal to also belong to category of the present invention, and scope of patent protection of the present invention should be defined by the claims.

Claims (5)

1. deep water shallow-layer fracture pressure computing technique, is characterized in that, the method comprises the following steps:

According to seismic interval velocity data and experimental data, determine deep water superficial part formation mechanical property;

The unified failure criterion of take is calculated the well week plastic zone stress state in well pressure process as yield criterion;

According to the theoretical well brill that calculates of the excess pore pressure in soil mechanics, open the excess pore pressure regularity of distribution that rear drilling well causes;

According to the theoretical effective stress of calculating wellbore of effective stress;

In conjunction with the theoretical fracture pressure of calculating deep water superficial part stratum of fracturing.

2. deep water shallow-layer fracture pressure computing technique as claimed in claim 1, is characterized in that, utilizes the not feature of fixed diagenesis of deep water superficial part stratum in the method, adopts the method that soil mechanics theory and drilling engineering combine to calculate deep water superficial part formation fracture pressure.

3. deep water shallow-layer fracture pressure computing technique as claimed in claim 1 or 2, it is characterized in that, in the method deep water superficial part stratum mechanical characteristic definite be based on GB < < Standard for test methods of earthworks (GB_T50123-19993) > >, the intensity of shallow sediment adopts total stress intensity index to calculate.

4. deep water shallow-layer fracture pressure computing technique as claimed in claim 1, it is characterized in that, the method has taked the excess pore pressure in soil mechanics theoretical to the calculating of all pore pressures of well in drilling process: well is bored the change that meeting causes well week reservoir stress, part stress can the pore pressure in stratum be born, and causes the change of formation pore pressure.By changed the pore pressure change amount causing by external applied load, be called excess pore pressure, be denoted as Δ P, its expression formula is

ΔP=P _p-P _p0=βΔσ _oct+(2.12A-0.71)Δτ _oct (1)

Wherein,

During drilling well, plastic zone excess pore pressure is

In formula: α and β are Henkel pore pressure coefficient, for saturated soil, get β=1; A is Skempton excess pore pressure coefficient; σ _hfor stress flatly.

5. deep water shallow-layer fracture pressure computing technique as claimed in claim 1, it is characterized in that, the method that the method adopts excess pore pressure and fracturing theory to combine to the calculating of deep water shallow-layer fracture pressure, when the pore pressure in deep water shallow-layer saturated soil body unit equals to act on the external pressure on this element, the soil body is in critical condition, when pore pressure surpasses threshold, effective stress in the soil body will become tensile stress, if tensile stress surpasses the tensile strength of the soil body, to ftracture in stratum, when pit shaft breaks, should meet fringe conditions

In formula, St is stratum tensile strength.

Tangential effective stress on the borehole wall is

Deep water shallow-layer pit shaft fracture pressure is

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